Massaprosenteina

Massaprosenteina, or mass percent, is a way to express the composition of a mixture by comparing the mass of a component to the total mass of the mixture. It is defined as w_i% = (m_i / M_total) × 100, where m_i is the mass of component i and M_total is the sum of all component masses. The corresponding dimensionless quantity is the mass fraction w_i = m_i / M_total.

Mass percent is related to other concentration measures, such as mole percent x_i = n_i / Σ n_j, where n_i is the amount in moles. The two are connected by w_i = (x_i M_i) / (Σ x_j M_j) × 100, where M_i is the molar mass of component i. Conversely, given mass percentages and molar masses, one can derive mole fractions.

An example: a mixture contains 25 g ethanol (M ≈ 46.07 g/mol) and 75 g water (M ≈ 18.015 g/mol). The total mass is 100 g, so ethanol has a mass percent of 25% and water 75%. The corresponding mole quantities are n_ethanol ≈ 0.543 mol and n_water ≈ 4.164 mol, yielding mole fractions after normalization.

Mass percent is widely used in chemical formulations, fuels, alloys, and pharmaceuticals because it is straightforward to determine gravimetrically and is not directly affected by temperature in the way volume-based concentrations are. It is important to note that mass percent alone does not convey information about the number of particles or thermodynamic properties; these require additional data such as molar masses or densities.